Flexible, porous substrates are frequently consolidated or strengthened by treating them with a polymeric binder. Flexible, porous substrates such as, for example, paper, woven fabrics, and nonwoven fabrics, are frequently treated with solutions or dispersions containing polymeric binders in order to impart improved properties. Properties such as, for example, resiliency, crock resistance, dryclean resistance, wash durability, tear strength, fold endurance, and the like, may be improved by applying a polymeric binder to flexible, porous substrates where the binder is disposed in or on the substrate.
In many instances it is desirable to apply an aqueous solution or dispersion containing a polymeric binder to a flexible, porous substrate, wherein the binder is present in a substantially thermoplastic, or substantially uncrosslinked, state, in order that flow, penetration, film formation, and the like, may occur after the binder solution or dispersion has contacted the substrate. It is also frequently desirable to effect crosslinking once the binder has achieved its final location, or concurrently with the drying process, in order to enhance the properties of the treated substrate. Many of the conventional crosslinking agents such as, for example, copolymerized N-methylol acrylamide and added urea/formaldehyde resins inherently contain or liberate formaldehyde, a skin and eye irritant, a mutagen, and a suspect carcinogen. A formaldehyde-free binder which is capable of effective crosslinking is needed for the treatment of porous substrates. The improved method of this invention for treating a flexible, porous substrate with a formaldehyde-free composition solves this problem.